1. Field of the Invention
The present invention relates to a substrate processing apparatus, in particular to a structure of a processing tank for use in processing a substrate by immersing the substrate in a processing liquid held in the tank.
2. Background Art
In the past, the substrate processing apparatuses have been widely used, for providing various processes, such as etching, cleaning and the like, to a substrate, such as a semiconductor wafer, a glass substrate and the like. As one example of such substrate processing apparatuses, an apparatus has been known, which is configured for providing a process to multiple sheets of substrates, at a time, by storing or accommodating in advance the processing liquid, such as an etching liquid, a cleaning liquid or the like, in the processing tank, and then immersing the multiple sheets of substrates into the processing liquid stored or accommodated in the processing tank while the substrates are supported by a substrate support member.
In such a substrate processing apparatus, a pair of left and right nozzles are provided at a lower portion of the processing tank, while a top end portion of the processing tank is opened. Thus, the processing liquid supplied from each nozzle can overflow from the top end opening of the processing tank.
In this substrate processing apparatus, the processing liquid supplied from the nozzles first flows upward in the processing tank, and then flows toward each of the side walls of the processing tank along the surface of the processing liquid in the vicinity of the top end opening of the processing tank. As a result, a part of the processing liquid overflows an upper edge of each of the side walls of the processing tank and is then discharged from the processing tank. Meanwhile, another part of the processing liquid collides with the upper edge portion of the processing tank and then flows downward into the processing tank along each of the side walls of the tank, without overflowing the upper edge portion.
In the vicinity of the surface of the processing liquid, foreign matter, such as dust coming from the outside of the processing tank, mist of a chemical liquid and the like, may tend to flow in the processing liquid. In addition, in the vicinity of the surface of the processing liquid, the air (or oxygen) present in the atmosphere of the processing tank will be mixed with the processing liquid. Thus, there is a risk that such foreign matter and/or air may be transferred deep into the processing tank, together with the processing liquid that will flow again into the processing tank after flowing along the surface of the liquid in the vicinity of the top end opening of the tank. Such foreign matter may contaminate the substrates, leading to a non-uniform process to the substrates and an unduly lowered processing speed.
To address such problems, one measure, as disclosed in JP2006-179758A, has been known. The entire contents of JP2006-179758A are incorporated herein by reference. In the substrate processing apparatus disclosed in this patent document, as shown in FIG. 6, a pair of left and right nozzles 102, 103 are provided to a lower portion of a processing tank 101, such that the processing liquid supplied from each nozzle 102, 103 can be accommodated in the tank 101. Then, substrates 105 are immersed into the processing liquid while being held by a substrate holding member 104. In this way, a desired process can be provided to the substrates 105. Furthermore, in the substrate processing apparatus disclosed in JP2006-179758A, projecting portions 106, 107, each projecting outward from an upper end portion of the processing tank 101, are provided. This configuration can facilitate discharge of the processing liquid via each projecting portion 106, 107 after the liquid flows along the surface thereof in the vicinity of the top end opening of the processing tank 101.
However, in the substrate processing apparatus disclosed in JP2006-179758A, only the projecting portions 106, 107 are provided to the upper end portion of the processing tank 101. As a result, the processing liquid will flows in the processing tank 101, as schematically shown in FIG. 6. More specifically, as depicted by arrows 108, 109 in FIG. 6, a first part of the processing liquid first flows upward in the processing tank around a central portion, in the lateral direction (substrate-plane direction), of each substrate 105 and then flows from the central portion toward the outside in the lateral direction in the vicinity of the surface of the processing liquid along the surface thereof. In addition, as depicted by arrows 110, 111, 112, 113 in FIG. 6, a second part of the processing liquid first flows upward in the processing tank, laterally outside the central portion of each substrate 105, and then flows slightly below the surface of the processing liquid. In this case, the first part of the processing liquid will collide with the second part of the processing liquid in the vicinity of each projecting portion 106, 107. As a result, backflow or turbulence of the processing liquid is likely to occur around each projecting portion 106, 107.
Therefore, in the substrate processing apparatus according to JP2006-179758A, the first part of the processing liquid that flows from the central portion to the outside in the lateral direction in the vicinity of the surface of the processing liquid along the surface thereof (or the processing liquid that flows as depicted by each arrow 109), i.e., the processing liquid that may capture the foreign matter and/or oxygen in the vicinity of the surface thereof, may tend to be returned deep into the processing tank 101, without being discharged from each projecting portion 106, 107. This may cause contamination of the substrates, non-uniformity of the process and unwanted lowering of the processing speed.